High efficiency modular cryocooler with floating piston expander

Abstract

A compact, modular, cryocooler is provided for use in relatively small-scale applications, i.e., applications requiring less than approximately 10 Watts of cooling capacity at about 10 degrees K or less. The cryocooler 10 utilizes a recuperative heat exchanger integrally combined with a floating piston expander having a piston adapted for periodic movement within an expansion cylinder. The piston is actuatable without an external drive mechanism, but rather by selective operation of processor controlled “smart”, variable current pulse valves which serve to alternately couple working fluid and ballast fluid to opposite ends of the cylinder. The valves are actuated in response to output signals generated by a non-invasive inductive sensor, which detects the position of the piston within the cylinder. The combination of the floating piston expander, as precisely controlled by the sensor, smart valves and a processor, with the recuperative heat exchanger, provides improved thermal efficiency relative to conventional small scale cryocoolers which typically utilize regenerative heat exchangers. The floating piston expander and recuperative heat exchanger are fabricated as an integrated, modular unit, which facilitates scaling to N modular units. Only a single flow-path is required to connect adjacent modular units to advantageously simplify both scaling and manifold construction.